Radio lan communication system

ABSTRACT

A wireless LAN communication system includes a base stations having terminals respectively associated with the base stations and managed by a network management system. In the wireless LAN communication system, each of the base stations includes an association information transmitting function for transmitting association information for a terminal to the terminal through a beacon, and each of the terminals includes an association set destination base station selecting function for selecting an association set destination base station based on the association information transmitted from the base station. Based on the association information transmitted by the base station, the terminal autonomously selects a connection destination base station to perform load sharing.

TECHNICAL FIELD

The present invention relates to a wireless LAN communication system,and more particularly to load sharing (load balance) among basestations.

BACKGROUND ART

In a conventional wireless LAN communication system of this kind, when abase station has traffic larger than a specified value, the base stationselects a terminal having traffic larger than a specified value fromterminals connected to the base station and switches the channel of theselected terminal and a channel of another base station having trafficsmaller than the specified value. In this case, the channel of the basestation having traffic smaller than the specified value is determinedaccording to a result of monitoring by a receiver for monitoring otherchannels, provided for each base station (see JP 2001-237856 A, forexample).

In the above-described conventional load sharing among base stations ina wireless LAN communication system, to perform channel changeover,respective base stations need to monitor the other channels to determinea channel of another base station having traffic smaller than thespecified value.

The present invention has been made to solve the problem describedabove, and has an object to provide a wireless LAN communication systemcapable of performing load sharing among base stations in which aterminal autonomously selects a connection destination base stationbased on information on the number of associations transmitted from eachof the base stations.

DISCLOSURE OF THE INVENTION

In view of the above object, the present invention provides a wirelessLAN communication system, including a plurality of base stations eachhaving terminals which are set to be associated therewith and managed byan NMS, the wireless LAN communication system being characterized inthat: each of the base stations includes an association informationtransmitting function for transmitting association information for aterminal to the terminal by a beacon; and each of the terminals includesan association set destination base station selecting function forselecting an association set destination base station based on theassociation information transmitted from the base station.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically showing a configuration of a wirelessLAN communication system according to an embodiment of the presentinvention;

FIG. 2 is a flowchart showing an example of an operation performed by abase station in the wireless LAN communication system according to thepresent invention;

FIG. 3 is a flowchart showing an example of an operation performed by aterminal in the wireless LAN communication system according to thepresent invention;

FIG. 4 is a flowchart showing an example of an operation to select anassociation destination base station in FIG. 3;

FIG. 5 is a flowchart showing an example of an operation performed by anNMS in the wireless LAN communication system according to the presentinvention;

FIG. 6 is a diagram for explaining base station forcible changeover inthe wireless LAN communication system according to the presentinvention; and

FIG. 7 is a flowchart showing an example of an operation of a basestation forcible changeover in the wireless LAN communication systemaccording to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 schematically shows a configuration of a wireless LANcommunication system according to the present invention. A plurality ofwireless base stations AP1 to AP3 (for example, three stations herein)are connected to an NMS (network management system) via a wired networkNW. Radio communications WT are performed between the wireless basestations AP1 to AP3 and a terminal T. In practice, a great number ofterminals T are separately associated with each of the base stations AP1to AP3.

In the present invention, the terminal T autonomously selects aconnection destination base station based on information on the numberof associations transmitted from each of the base stations AP1 to AP3 tobalance loads of the base stations AP1 to AP3. At this time, in order tobalance the loads of the base stations AP1 to AP3, connection terminalsT are accommodated in a balanced manner. This prevents extreme load biaswhen a new base station is added in an identical service area due to anincrease in traffic, and other cases. In addition, in order to ensureVoIP (audio data) quality, VoIP registration users are assigned to aplurality of base stations in a balanced manner.

The base stations AP1 to AP3 notify the terminal T of remainingassociation counts (association information) by beacon frames. Theterminal T determines an association set destination base station basedon the remaining association counts notified by the base stations AP1 toAP3 and/or radio reception conditions (RSSI (radio-wave level), PER(communication quality: packet error rate)) with respect to the basestations AP1 to AP3. In other words, the terminal T selects the best AP(access point) based on the load sharing in which loads are evenlybalanced among the base stations.

Note that a remaining association count generally represents a valueobtained by subtracting the number of associated terminals from thenumber of terminals to which IP addresses are assigned. Whencommunications are preferentially performed for a group of particularterminals, the remaining association count may be obtained from theformula (the number of terminals to which IP addresses areassigned)—(the number of terminals belonging to a particular groupassociated), with the number of terminals other than terminals belongingto a particular group being excluded.

Automatic Base Station Selection

According to the present invention, each of the base stations AP1 to AP3sets the remaining association count in a beacon frame and transmits thebeacon frame. The base stations AP1 to AP3 accept an association setrequest from the terminal T unless the maximum number of associations isexceeded. When the number of associations exceeds its threshold value,the base stations AP1 to AP3 notify the NMS of the state by a trap viathe network.

FIG. 2 shows an operational flowchart of each of the base stations AP1to AP3 in FIG. 1. Each of the base stations AP1 to AP3 sets theremaining association count in a beacon frame and transmits the beaconframe to each terminal T (Step S21). When an association (set) requestis transmitted from a terminal T (Step S22), each base station judgeswhether the maximum number of associations is exceeded (Step S23). Whenthe maximum number of associations is not exceeded, the base stationaccepts the terminal T (Step S24). Then, the base station judges whethera predetermined association-count threshold value (a number smaller thanthe maximum number of associations) is exceeded (Step S25). When thepredetermined association-count threshold value is exceeded, the basestation notifies the NMS by transmitting a trap via the network NW thatthe association-count threshold value is exceeded (Step S26).

FIG. 3 shows an operational flowchart of the terminal T in FIG. 1. Theterminal T first takes in the remaining association counts of the basestations notified with beacon frames by the base stations AP1 to AP3(Step S31), and then selects an association destination base stationaccording to these remaining association counts and, as needed, alsoradio reception conditions (RSSI, PER) with respect to the base stations(Step S32). A function of detecting radio reception conditions (RSSI,PER) is normally provided in the terminal T.

An association destination base station is selected so as to select thebest AP based on load sharing. When an association destination basestation is selected, the priority of the base stations AP1 to AP3 isdetermined according to the remaining association counts, as shown inFIG. 4 (Step S321). When a priority-connection base station has beenset, the highest priority is given to that base station (Step S322).When forcible changeover to be described later is instructed, a basestation which has been connected is given the lowest priority (StepS323).

Returning to FIG. 3, after an association destination base station isselected, the terminal T associates with a base station having higherpriority (Step S33). If the terminal T cannot associate with that basestation (Step S34), the terminal T assigns the lowest priority to thebase station with which the terminal T has tried to associate (StepS35). The terminal T returns to Step S32 to select an associationdestination base station again.

FIG. 5 shows an operational flowchart of the NMS in FIG. 1. Although theNMS is not involved in the selection of a base station by the terminalT, the NMS regularly monitors the loads (the amount of traffic such asthe number of transfer packets) of the base stations AP1 to AP3 asstatistical information and monitors respective association-countthreshold values by traps. Upon reception of a notification indicatingthat the association-count threshold value is exceeded (Step S51), theNMS informs an operator of the notification (by displaying on a monitorscreen, for example) (Step S52). When the operator inputs to instructforcible changeover (Step S53), the NMS instructs, via the base station,the corresponding terminal to perform forcible changeover (Step S54).The forcible changeover will be described later.

Note that since VoIP (audio data) is required to be immediatelytransmitted, it largely uses wireless resources and causes an increasein load at a base station. Accordingly, from a point of view that VoIPusers are assigned in a balanced manner to a plurality of base stationsin order to ensure VoIP (audio data) quality, the VoIP users areregistered in advance in the system side as VoIP registration users, andrespective base stations grasp the number of VoIP registration users aswell as the number of associations. In such a system, a remaining VoIPregistration user count may be combined with the remaining associationcount as association information. Alternatively, the remaining VoIPregistration user count may be used in place of the remainingassociation count.

In this case, the base stations notify a terminal of the remainingassociation counts and the remaining VoIP registration user counts bybeacon frames, and the terminal determines an association destinationbase station based on the radio reception conditions (RSSI, PER), andthe remaining association counts and the remaining VoIP registrationuser counts, which have been notified by the base stations.

Here, a remaining VoIP registration user count represents the number ofVoIP users who can be further registered at a base station thatregisters VoIP users, that is, a remaining VoIP registration user countwith respect to the number of maximum VoIP registration users in asystem where audio data is extracted from communication data; QoSparameters are provided to control the audio data and ordinary dataseparately from each other; the audio data, that is, VoIP, iscontrolled, for example, with the highest communication priority; andfurther, users using VoIP are registered as VoIP registration users tothereby evenly balance the loads of the base stations. Note that thepresent invention can be applied to a system where a user using VoIP isregistered as a VoIP registration user, so the system does notnecessarily have to control VoIP is with the highest priority.

Then, each of the base stations AP1 to AP3 sets the remainingassociation count and the remaining VoIP registration user count in abeacon frame and transmits the beacon frame. The base stations AP1 toAP3 accept an association set request from the terminal T unless themaximum number of associations is exceeded. When the number ofassociations and the number of VoIP registration users exceed theirthreshold values, the base stations AP1 to AP3 notify the NMS of thestate by a trap.

The terminal T determines a base station to be connected from the basestations AP1 to AP3 based on the radio reception conditions (RSSI, PER)with respect to the base stations AP1 to AP3, and the remainingassociation counts and the remaining VoIP registration user counts atthe base stations AP1 to AP3, which have been notified with beaconframes by the base stations AP1 to AP3. Then, the terminal T sets anassociation with the determined base station.

An algorithm procedure applied to the selection of an associationdestination base station from the base stations AP1 to AP3 can bechanged according to a firmware upgrade or the like. For example: 1) abase station having a larger remaining VoIP registration user count isselected; 2) a base station having a larger remaining association countis selected when base stations have the same remaining VoIP registrationuser count; and 3) a base station is selected randomly when basestations have the same remaining association count. Other factors arebasically the same as those described above.

Forcible Changeover of Base Station

A forcible changeover function for changing over a connectiondestination base station of the terminal T is provided in order toadjust loads among the plurality of base stations AP1 to AP3 accordingto an instruction of the operator when a new base station is added orwhen bias is detected in the number of associations, the number of VoIPregistration users, or the amount of traffic during a stationaryoperation.

FIG. 6 is a diagram of the wireless LAN communication system accordingto the present invention, for explaining the base station forciblechangeover. FIG. 7 is a sequence of the base station forciblechangeover. A changeover sequence will be described with reference toFIGS. 6 and 7.

In the NMS, the operator monitors, on a screen display or the like, thenumbers of transfer packets (traffic information) which are periodicallycollected from the base stations AP1 to AP3 to check whether the trafficamong the base stations is balanced or not. At the same time, theoperator obtains the numbers of associations and the numbers of VoIPregistration users of the base stations from association logs. As aresult, when it is determined that a connection destination base stationof the terminal needs to be changed over, the following procedure fromstep (a) is executed based on the operator's judgment.

In addition, when the network configuration is changed, for example, byadding a new base station, and when a trap indicating that the thresholdvalues are exceeded (for the number of associations and the number ofVoIP registration users) is received from a base station, the followingprocedure from step (a) is executed based on the operator's judgment.

(a) Under the above-described situations, when the operator judges inthe NMS that forcible changeover is necessary and inputs to a computerof the NMS an instruction for the forcible changeover, the forciblechangeover is started to make a terminal forcible disassociation request(a disassociation request transmission instruction) to cause the basestation AP3 which is an association set destination of the targetterminal T to transmit a disassociation request to the target terminalT. The NMS knows the association terminals of each of the base stationsfrom normal communications and information periodically collected fromthe base stations.

(b) The base station AP3 transmits a disassociation request to thetarget terminal T, and returns a terminal forcible disassociationresponse to the NMS.

(c) The terminal T returns a response to the disassociation request,then starts the procedure of the above-described best AP selection basedon load sharing to search for a base station by transferring anassociation request and an association response, and determines a newassociation set destination (for example, the base station AP2). Notethat the terminal T holds the radio reception conditions (RSSI, PER) ofall base stations measured during execution of the above procedure.

(d) After completion of the changeover, the NMS makes an inquiry to theterminal T via the new association destination base station AP2 aboutthe radio condition of the base station which was measured during theprocedure of “connection destination AP changeover processing” bytransferring a site survey request and a site survey response (when theoperator judges that it is necessary).

According to the present invention as described above, there is provideda wireless LAN communication system, including a plurality of basestations each having terminals which are set to be associated therewithand managed by an NMS, the wireless LAN communication system beingcharacterized in that: each of the base stations has an associationinformation transmitting function for transmitting associationinformation for a terminal to the terminal by a beacon; and each of theterminals has an association set destination base station selectingfunction for selecting an association set destination base station basedon the association information transmitted from the base station.Therefore, load sharing is realized among base stations in which aterminal autonomously selects a connection destination base stationbased on association information transmitted from each of the basestations.

INDUSTRIAL APPLICABILITY

The present invention can be basically applied to all wireless LANcommunication systems.

1. A wireless LAN communication system, comprising a plurality of basestations, each base station having terminals which are associated withthe respective base stations, the base stations being managed by an NMS(network management system), wherein each of the base stations comprisesassociation information transmitting means for transmitting associationinformation for a terminal to the terminal through a beacon, each of theterminals comprises association set destination base station selectingmeans for selecting an association set destination base station based onthe association information transmitted from the base station, a VoIPuser who transfers audio data is registered as a VoIP registration userin advance, and the association information includes a remaining VoIPregistration user count at the base station.
 2. The wireless LANcommunication system according to claim 1, wherein each base stationfurther comprises association count excess notifying means for notifyingthe NMS through a trap when an association count for a terminal exceedsa predetermined value.
 3. The wireless LAN communication systemaccording to claim 2, wherein the association information includes aremaining association count at the base station.
 4. The wireless LANcommunication system according to claim 2, wherein the associationinformation includes the remaining VoIP registration user count and theremaining association count at the base station, and the association setdestination base station is selected by the association set destinationbase station selecting means of the terminal based on the remaining VoIPregistration user count and the remaining association count.
 5. Thewireless LAN communication system according to claim 1, wherein theassociation information includes a remaining association count at thebase station.
 6. The wireless LAN communication system according toclaim 1, wherein the association information includes the remaining VoIPregistration user count and the remaining association count at the basestation, and the association set destination base station is selected bythe association set destination base station selecting means of theterminal based on the remaining VoIP registration user count and theremaining association count.
 7. The wireless LAN communication systemaccording to claim 1, wherein the NMS comprises disassociation requesttransmission instructing means for causing a base station to transmit adisassociation request to a terminal according to an instruction inputby an operator and, in response to the instruction, the base station andthe terminal select an association set destination base station usingthe association information transmitting means and the association setdestination base station selecting means, respectively.